问题
I need to access ModelState in Asp.net Core 2.1 Middleware, but this is just accessible from Controller.
For example I have ResponseFormatterMiddleware and in this Middleware I need to ignore ModelState error and show it's errors in 'Response Message':
public class ResponseFormatterMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<ResponseFormatterMiddleware> _logger;
public ResponseFormatterMiddleware(RequestDelegate next, ILoggerFactory loggerFactory)
{
_next = next ?? throw new ArgumentNullException(nameof(next));
_logger = loggerFactory?.CreateLogger<ResponseFormatterMiddleware>() ?? throw new ArgumentNullException(nameof(loggerFactory));
}
public async Task Invoke(HttpContext context)
{
var originBody = context.Response.Body;
using (var responseBody = new MemoryStream())
{
context.Response.Body = responseBody;
// Process inner middlewares and return result.
await _next(context);
responseBody.Seek(0, SeekOrigin.Begin);
using (var streamReader = new StreamReader(responseBody))
{
// Get action result come from mvc pipeline
var strActionResult = streamReader.ReadToEnd();
var objActionResult = JsonConvert.DeserializeObject(strActionResult);
context.Response.Body = originBody;
// if (!ModelState.IsValid) => Get error message
// Create uniuqe shape for all responses.
var responseModel = new GenericResponseModel(objActionResult, (HttpStatusCode)context.Response.StatusCode, context.Items?["Message"]?.ToString());
// Set all response code to 200 and keep actual status code inside wrapped object.
context.Response.StatusCode = (int)HttpStatusCode.OK;
context.Response.ContentType = "application/json";
await context.Response.WriteAsync(JsonConvert.SerializeObject(responseModel));
}
}
}
}
// Extension method used to add the middleware to the HTTP request pipeline.
public static class ResponseFormatterMiddlewareExtensions
{
public static IApplicationBuilder UseResponseFormatter(this IApplicationBuilder builder)
{
return builder.UseMiddleware<ResponseFormatterMiddleware>();
}
}
[Serializable]
[DataContract]
public class GenericResponseModel
{
public GenericResponseModel(object result, HttpStatusCode statusCode, string message)
{
StatusCode = (int)statusCode;
Result = result;
Message = message;
}
[DataMember(Name = "result")]
public object Result { get; set; }
[DataMember(Name = "statusCode")]
public int StatusCode { get; set; }
[DataMember(Name = "message")]
public string Message { get; set; }
[DataMember(Name = "version")]
public string Version { get; set; } = "V1.0"
}
and this is my excpected result:
{
"result": null,
"statusCode": 400,
"message": "Name is required",
"version": "V1"
}
but now the observed result is:
{
"result": {
"Name": [
"Name is required"
]
},
"statusCode": 400,
"message": null,
"version": "V1"
}
回答1:
ModelState is only available after model binding . Just store the ModelState automatically with an action filter , thus you can use it within middleware .
Firstly , add a action filter to set the ModelState as an feature :
public class ModelStateFeatureFilter : IAsyncActionFilter
{
public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
var state = context.ModelState;
context.HttpContext.Features.Set<ModelStateFeature>(new ModelStateFeature(state));
await next();
}
}
Here the ModelStateFeature is a dummy class that holds the ModelState:
public class ModelStateFeature
{
public ModelStateDictionary ModelState { get; set; }
public ModelStateFeature(ModelStateDictionary state)
{
this.ModelState= state;
}
}
to make the action filter take place automatically , we need configure the MVC
services.AddMvc(opts=> {
opts.Filters.Add(typeof(ModelStateFeatureFilter));
})
And now we can use the ModelState within your Middleware as below:
public class ResponseFormatterMiddleware
{
// ...
public async Task Invoke(HttpContext context)
{
var originBody = context.Response.Body;
using (var responseBody = new MemoryStream())
{
context.Response.Body = responseBody;
// Process inner middlewares and return result.
await _next(context);
var ModelState = context.Features.Get<ModelStateFeature>()?.ModelState;
if (ModelState==null) {
return ; // if you need pass by , just set another flag in feature .
}
responseBody.Seek(0, SeekOrigin.Begin);
using (var streamReader = new StreamReader(responseBody))
{
// Get action result come from mvc pipeline
var strActionResult = streamReader.ReadToEnd();
var objActionResult = JsonConvert.DeserializeObject(strActionResult);
context.Response.Body = originBody;
// Create uniuqe shape for all responses.
var responseModel = new GenericResponseModel(objActionResult, (HttpStatusCode)context.Response.StatusCode, context.Items?["Message"]?.ToString());
// => Get error message
if (!ModelState.IsValid)
{
var errors= ModelState.Values.Where(v => v.Errors.Count > 0)
.SelectMany(v=>v.Errors)
.Select(v=>v.ErrorMessage)
.ToList();
responseModel.Result = null;
responseModel.Message = String.Join(" ; ",errors) ;
}
// Set all response code to 200 and keep actual status code inside wrapped object.
context.Response.StatusCode = (int)HttpStatusCode.OK;
context.Response.ContentType = "application/json";
await context.Response.WriteAsync(JsonConvert.SerializeObject(responseModel));
}
}
}
}
Let's test with a simple Model
public class MyModel {
[MinLength(6)]
[MaxLength(12)]
public string Name { get; set; }
public int Age { get; set; }
}
and a simple controller:
public class HomeController : Controller
{
public IActionResult Index(string name)
{
return new JsonResult(new {
Name=name
});
}
[HttpPost]
public IActionResult Person([Bind("Age,Name")]MyModel model)
{
return new JsonResult(model);
}
}
If we send a request with a valid payload :
POST https://localhost:44386/Home/Person HTTP/1.1
content-type: application/x-www-form-urlencoded
name=helloo&age=20
the response will be :
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/json
Server: Kestrel
X-SourceFiles: =?UTF-8?B?RDpccmVwb3J0XDIwMThcOVw5LTE4XEFwcFxBcHBcQXBwXEhvbWVcUGVyc29u?=
X-Powered-By: ASP.NET
{
"result": {
"name": "helloo",
"age": 20
},
"statusCode": 200,
"message": null,
"version": "V1.0"
}
And if we send a request with an invalid model :
POST https://localhost:44386/Home/Person HTTP/1.1
content-type: application/x-www-form-urlencoded
name=hello&age=i20
the response will be
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/json
Server: Kestrel
X-SourceFiles: =?UTF-8?B?RDpccmVwb3J0XDIwMThcOVw5LTE4XEFwcFxBcHBcQXBwXEhvbWVcUGVyc29u?=
X-Powered-By: ASP.NET
{
"result": null,
"statusCode": 200,
"message": "The value 'i20' is not valid for Age. ; The field Name must be a string or array type with a minimum length of '6'.",
"version": "V1.0"
}
回答2:
If you are implementing something like action filter, you can access it via context parameter of overriden method OnActionExecuting of 'ActionFilterAttribute' base class
public class ModelStateValidationFilter : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext context)
{
// You can access it via context.ModelState
ModelState.AddModelError("YourFieldName", "Error details...");
base.OnActionExecuting(context);
}
}
来源：https://stackoverflow.com/questions/52370655/access-modelstate-in-asp-net-core-middleware